Frame for constructing a hemispherical multi-layered shell

ABSTRACT

A plurality of annular plates are machined to have substantially identical outer diameters equal to the inner diameter of the head to be made. A first annular plate is arranged as an annular base plate. The other annular plates are cut into four congruent arc portions of less than 90° and braces are attached to each congruent arc portion. A plurality of the arc portions are mounted by a first end to the upper surface of the annular base plate in a substantially equally, circumferentially spaced arrangement. The second end of each arc portion is fastened to the outer surface of a central collar to form the hemispherical frame.

This is a division of application Ser. No. 262,422 filed May 11, 1981,now U.S. Pat. No. 4,403,387.

TECHNICAL FIELD

This invention relates to the construction of multi-layered pressurevessels. This invention specifically relates to frames for constructinga multi-layered vessel having a hemispherical head or a multi-layerspherical vessel.

BACKGROUND OF THE INVENTION

Pressure vessels are used for a large number of industrial applications.Pressure vessel walls may be constructed of a single layer or ofmultiple layers. Often a pressure vessel will contain one or morehemispherical heads because of the structural strength of ahemispherical shape. Such multi-layer pressure vessels are disclosed inU.S. Pat. Nos. 3,774,296, 3,785,040, 3,604,587 and 3,432,820. In singlewall vessels, a hemispherical shape may be cast or milled as a singleunit. In multi-layer shells, hemispherical heads are sometimes formedaround a hemispherical inner layer by welding on successive layers ofgores onto the inner layer in the fashion disclosed in U.S. Pat. Nos.3,374,935 and 3,423,820. Typically, the main support during themanufacture of the hemispherical head is a hemispherical frame. Suchframes have been formed by cutting arc segments from plate metal andwelding a hemispherical frame from such arcs onto a base plate. Becauseof the imprecise nature of cutting, the hemispherical frame formed isnot perfect and the construction of the head is made more difficult bythe need to correct for such deficiencies during construction.

In addition, the depth of each arc segment required to provide thenecessary strength for the frame produces a heavy frame which isdifficult to dismantle. If, as is sometimes necessary, the frame mustremain in place until the whole vessel is built, the frame must be cutby torch into small enough pieces to be withdrawn through an accesshatch.

Because pressure vessels are often one-of-a-kind constructions, moreexpensive techniques of forming more perfect hemispherical frames bycasting or machining are not economical. Therefore, with the prior art,the vessel manufacturer was faced with the choice of manufacturing amore precise and expensive frame or the more economical but lessaccurate frame for making the head.

SUMMARY OF THE INVENTION

A plurality of annular plates are machined to have substantiallyidentical outer diameters equal to the inner diameter of the head to bemade. A first annular plate is arranged as an annular base plate. Theother annular plates are cut into four congruent arc portions of lessthan 90° and braces are attached to each congruent arc portion. Aplurality of the arc positions are mounted by a first end to the uppersurface of the annular base plate in a substantially equally,circumferentially spaced arrangement. The second end of each arc portionis fastened to the outer surface of a central collar to form thehemispherical frame.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of stacked annular plates aftermilling;

FIG. 2 is a top view of an annular plate, with braces mounted, preparedfor cutting into four arc portions;

FIG. 3 is a side view partly in cross-section of the completed frame;and

FIG. 4 is a top view of the completed frame.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings and in particular FIGS. 3 and 4, the letter Fgenerally designates the completely assembled frame for the manufactureof a multi-layer head for a cylindrical multi-layer vessel. It should beunderstood that the frame F and the method of manufacture of the frame Fcannot only be used for manufacture of a multi-layered hemisphericalhead, but also for the manufacture of a spherical head or other curvedor dome-shaped vessel sections. Hereinafter, this disclosure willdiscuss the fabrication of a hemispherical head only but it should beunderstood that the principles discussed herein are applicable to suchother structures. FIG. 1 shows a plurality of annular plates 10 whichare machined to have a substantially equal outer diameter 12. The outerdiameter 12 of the annular plates 10 is equal to the desired innerdiameter of hemispherical head to be constructed. The width 14 of theannular plates 10 is chosen to provide sufficient strength. Because ofthe bracing, discussed below, the width 14 may be considerably less thanwould be necessary without bracing. A base plate 16 is taken from theplurality of annular plates 10 and arranged as the base for the frame Fof the present invention.

Each remaining annular plate 10 is cut into four substantially congruentarc portions 20 of less than 90°. A brace member 18 such as an angleiron is attached to each of the arc portions 20. As best seen in FIGS. 3and 4, a plurality of the arc portions 20 are mounted to the uppersurface 16a of base plate 16 by a first end 20a. The arc portions 20 arecircumferentially spaced equally around the annular base plate 16 anddirected radially inward. Each arc portion second end 20b is fastened tothe outer surface 22a of a central annular collar 22.

The preferred method of mounting the brace members 18 to the arcportions 20, as well as the arc portions 20 to the base plate 16 andcollar 22 is bolting. This allows easy disconnection of the bracemembers 18 and arc portions 20 when it is desired to remove the arcportions 20 from the completed head. Although the annular plates 10 maybe individually machined, it is most economical and accurate to stackthe plate metal to be machined and simultaneously machine the pluralityof annular plates 10. The brace members 18 may be added to the arcportions 20 before or after the arc portions 20 are cut from the annularplates 10.

Bracing means, generally designated as 36, include the brace member 18with first end 18a and second end 18b. The brace member first end 18a ismounted adjacent the arc portion first end 20a and the bracing membersecond 18b is mounted adjacent the arc portion second 20b. A brace plate38 is mounted to the brace member 18 substantially equal distance fromthe first end 18a and the second end 18b of the brace member 18. Fromthe brace plate 38 short bracing members or trusses 40 and 42 aremounted. The short bracing members first ends 40a and 42a are attachedto the brace plate 38. The short bracing means second ends 40b and 42bare mounted along the arc portion 20 such that the distances betweenbrace member first end 18a and short brace member second end 40b, shortbrace member second end 40b and short brace member second end 42b, andshort brace member second end 42b and brace member second end 18b willbe substantially equal. In the embodiment illustrated, the short bracemembers or trusses 40 and 42 are bolted to plate 38 and to the arcportion 20.

Because the desired frame F should have a diameter equal to the outerdiameter of the annular plates 10, each annular plate 10 will be firstcut at points 24 and 26 which are diametrically opposite. Four more cuts27, 28, 29 and 30 will be made to form four arc portions 20. The cutsare made so that the surface at the first end 20a of each arc portionwill be perpendicular to the surface at the second end 20b. The sectionremoved 32 between cuts 27 and 28 and the section 34 between cuts 29 and30 will have a length substantially equal to the outer diameter of thecollar 22. Therefore, when the arc portions 20 are mounted by the firstends 20a to base plate 16 upper surface 16a and the second ends 20b aremounted to the collar 22 (as shown in FIGS. 3 and 4), a hemisphericalsurface is formed of the outer curved edges 20c of each aligned arcportion 20.

The central collar 22 is a generally cylindrical member or ring of anouter diameter substantially equal to that of the length of the removedsegments 32 and 34. The outer surface 22a of the central collar 22 has aridge or shoulder 22b which receives and supports the ends 20b of eacharc portion 20 in alignment. Each arc portion end 20b has a stud 20dwelded on the underside to receive a bolt 33 which also extends throughthe collar 22. The arc portions 20 are mounted circumferentially,equally spaced along the base plate 16 and, therefore, are also mountedcircumferentially equally spaced about the collar 22. If the vessel tobe constructed is to have an opening in the hemispherical head, theopening may be formed about the collar 22.

The number of arc portions 20 to be mounted on the base plate 16 willdepend upon the radius of the head to be built and the size of the goresto be used. In a typical example, five annular plates or rings 10 willinitially be machined, with one being the base plate 16 and the otherfour being cut into sixteen arc portions 20 as shown in FIG. 4.

Once assembled, the frame F is placed within a partially constructedvessel, in a shop or elsewhere where it is necessary to fabricate thehemispherical head. Such fabrication is accomplished by the addition ofgores directly onto the arc portions to form a first layer. Though, asis known from prior patents such as those already discussed, the vesselhead is completed one layer at a time, one of the advantages of theframe F is that it may be finally assembled in the field and easilydisassembled and removed, even from inside a completed multi-layervessel.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof and various changes in the size,shape and materials as well as the details of the illustratedconstruction may be made without departing from the spirit of theinvention. For example, a frame for a spherical vessel may be made byjoining two hemispherical frames F together.

I claim:
 1. A jig frame for constructing a hemispherical multi-layeredshell, comprising:an annular ring-shaped base plate with a bottomsurface and a top surface; a plurality of arc portions cut from anannular ring-shaped plate congruent to said annular ring-shaped baseplate and having an outer radius of curvature equal to the outer radiusof curvature of said base plate, each with a first end and a second end;said plurality of arc portions mounted and detachably secured by saidfirst ends to said upper surface of said base plate equallycircumferentially spaced and radially directed; and said second end ofsaid arc portions being attached to the outer surface of a centralcollar whereby said arc portions are readily detachable from said baseplate after manufacturing said shell on said frame.
 2. The frame ofclaim 1, further including:a brace means for each arc portion.
 3. Theapparatus of claim 2, wherein said brace means includes:a brace memberwith a first end and a second end, said first end mounted adjacent saidfirst end of said arc portion and said second end mounted adjacent saidsecond end of said arc portion; a mounting plate mounted with said bracemember; first and second short braces each with a first end and a secondend; and said first end of said short braces mounted with said mountingplate and said second end of said first and said second short bracesmounted to said arc portion such that said ends of said braces mountedto said arc portion are spaced substantially equal distances along saidarc portion.
 4. The frame of claim 1, wherein:said arc portions aremounted to said base plate and said collar by bolts.
 5. The frame ofclaim 1, wherein:said first end of said arc portion has a first endsurface; said second end of said arc portion has a second end surface;and said first end surface and said second end surface are substantiallyperpendicular.
 6. The frame of claim 1, further including:a portion ofsaid collar forming a ridge which receives and supports said second endsof said arc portions; a stud depending from said arc portion second endsto receive a bolt; and said bolt extending through said stud and saidcollar to mount said arc portions to said collar.